Date: Wed, 25 Jul 2007 10:47:15 -0700 From: Bakul Shah <bakul@bitblocks.com> To: Doug Rabson <dfr@rabson.org> Cc: freebsd-fs@freebsd.org, Pawel Jakub Dawidek <pjd@freebsd.org>, Mark Powell <M.S.Powell@salford.ac.uk> Subject: Re: ZfS & GEOM with many odd drive sizes Message-ID: <20070725174715.9F47E5B3B@mail.bitblocks.com> In-Reply-To: Your message of "Wed, 25 Jul 2007 10:30:48 BST." <1185355848.3698.7.camel@herring.rabson.org>
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> If you do that, ZFS can use its checksums to continually > monitor the two sides of your mirrors for consistency and will be able > to notice as early as possible when one of the drives goes flakey. Does it really do this? As I understood it, only one of the disks in a mirror will be read for a given block. If the checksum fails, the same block from the other disk is read and checksummed. If all the disks in a mirror are read for every block, ZFS read performance would get somewhat worse instead of linear scaling up with more disks in a mirror. In order to monitor data on both disks one would need to periodically run "zpool scrub", no? But that is not *continuous* monitoring of the two sides.
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